Question: $ \left(\dfrac{9}{10}\right)^{-3}$
Answer: $= \left(\dfrac{10}{9}\right)^{3}$ $= \left(\dfrac{10}{9}\right)\cdot\left(\dfrac{10}{9}\right)\cdot \left(\dfrac{10}{9}\right)$ $= \dfrac{100}{81}\cdot\left(\dfrac{10}{9}\right)$ $= \dfrac{1000}{729}$